Process for producing a molded part

ABSTRACT

A method of manufacturing a molded part includes inserting melt into a cavity of a first tool part, and the first tool part and a second tool part are moved away from one another during or after the insertion of the melt by moving a mold clamping plate relative to a mold clamping plate such that in the first tool part or in a second tool part an at least partial clearance of a first or second zone of the cavity takes place, and a gap is formed between the first tool part and the second tool part. Melt is further inserted into the cleared area of the cavity, and the gap is bridged by an at least already partially solidified section of the melt. A holding force is transmitted from the second tool part through the partially solidified section of the melt bridging the gap to the first tool part.

The invention concerns a method to manufacture a molded part with the features of the preamble of claim 1.

In a generic method, the problem can arise that a molded part is to be produced, which requires a mass of melt exceeding a provided quantity that is supplied under one time by an injection unit of the molding machine. In order to solve this problem, it is known that the required amount of melt is inserted sequentially into the cavity by portion amounts, wherein the cavity for this purpose can be increased. The single portion amounts of melt can be provided successively fey a single injection unit or several injection units. For this purpose, shear edge tool have also become known. However, the dimensions of the molded part produced in this way were of course limited by the maximum enlargeability of the cavity, as a holding force had to be transferred between the mold parts in order to prevent melt from escaping from the cavity.

The object of the invention is to provide a generic method in which the above-mentioned limitation is overcome.

This object is solved by a method with the features of claim 1. Advantageous embodiments of the invention are defined in the dependent claims.

Since according to the invention, it is provided that the gap is bridged by an at least already partially solidified section of the melt, and a holding force is transferred from the second tool part through the at least already partially solidified section of the melt, bridging the gap to the first tool part, the limitation is eliminated by the maximum enlargeability of the cavity.

The first and second molded parts are moved away from each other by moving the second mold clamping plate relative to the first mold clamping plate.

Preferably, the molding machine is an injection molding machine, and the method for producing the molded part is an injection molding method. The melt is preferably a melt of e.g. thermoplastic material.

In contrast to an extrusion method, it is preferably provided: that the injection unit (or, if several injection units are provided, each of them separately) operates discontinuously. Of course, if is also possible to provide continuously operating injection units.

Of course, it would be possible to provide a cover bridging the gap between the first and second tool part. This cover can he made out of one piece with the first or second tool part, or connected to the first and second tool part. However, no holding force is transmitted through this cover. Whether with or without cover, the holding force is transmitted, at least partially, preferably exclusively via the section of the melt between the foot parts that bridges the gap, and is at least already partially solidified.

The tool parts can have guides, in this case there is no need for a guide of the movable mold clamping plate on the machine frame.

It is preferred to move the first tool part and the second tool part away from each other in a parallelism-controlled manner. This is particularly indicated if the cavity is asymmetrically shaped relative to the machine's longitudinal axis in such a way that there is no symmetrical swelling force relative to the machine's longitudinal axis.

A molded part of any desired length—endless, so to speak—can be produced if a Holding device is provided for the already solidified section of the injection-molded part, which supports it. It may be necessary to provide a passage opening in the second mold clamping plate through which the already solidified part of the molded part can pass through. The holding device can, but does not have to, be provided separately from the tool. In other words, the holding device can be formed wholly or partially by elements of the first and/or second tool part.

It may he intended to vary the holding force over time, depending on a momentary cross-section of the solidified section of the injection molded part.

With respect to a possible embodiment, additional force transmission elements are provided for partial, transmission of the holding force, so that the holding force does not have to be transmitted completely over the at least already partly solidified section of the melt.

Embodiments of the invention are discussed on the basis of the figures. Showing:

FIG. 1 a first molding machine after the insertion of a first amount of melt

FIG. 2 the molding machine shown in FIG. 1 after the first and second tool halves have been moved so far apart from each other that a gap is formed in between them

FIG. 3 a second molding machine before the insertion of a first amount of melt

FIG. 4 a third molding machine before the insertion of a first amount of melt

FIG. 5a-c a partial view of a fourth molding machine for producing molded parts unlimited in length

FIG. 1 shows a clamping unit 1 of a molding machine (here: two-plates injection molding machine) with a machine bed 2, a first mold clamping plate 3 fixed to the machine bed 2, and a second mold clamping plate 4 movable on the machine bed 2. In this embodiment, a cavity arranged around the machine's longitudinal axis is formed between a first tool pad 8, arranged on the first mold clamping plate 3, and a second tool part 9, arranged on the second mold clamping plate 4.

The method of the second mold damping plate 4 nan be performed by a rapid stroke mechanism, which is not shown because it is prior art. A holding force, which counteracts a swelling force exerted by the melt on the cavity, can be exerted on the tie bars 5 by means of pressure pads 7, and on the second mold clamping plate 4 by means of the locking device 6 (here, split locking nuts known per se).

In the state shown in FIG. 1, a first amount of melt was inserted into the cavity via an injection unit 13, which is not shown (but see FIGS. 3 and 4), and fills it completely. If the first amount of melt were to solidify in this elate, the dimensioning of the injection-molded part 10 shown would correspond to the dimensioning of the final molding part. However, according to the invention, the second mold clamping plate 4, and with it, the second tool part 9, are new moved so far away from the first mold clamping plate 3, and thus from the first mold part 8, that a gap 12 is formed between the first and second tool parts 8, 9, the size of which is limited by the maximum stroke of the pressure pads 7.

The moving away can take place either with the locking device 8 closed or with it open.

Of course, the movement away can only take place when the first amount of melt has solidified at least to such an extent that it can bridge the gap 12 with the sufficiently solidified section, and can transfer holding force at feast partially.

During the injection of the second amount of melt, the holding force generated by the pressure pad 7 is transmitted through the sufficiently solidified section. After reaching the maximum stroke of the pressure pads 7, the tie bars 5 are moved so far by the pressure pads 7 that the stroke of the pressure pads 7 is available again. If the locking device 6 was open, it is closed, and the second amount of melt is inserted into the cleared zone of the cavity, which here is formed exclusively in the first tool part 8. This process can be repeated until the end of the lockable area of the tie bars 5 is reached. Then the molded part is produced with its maximum possible dimensioning.

In contrast to the clamping unit 1 shown in FIGS. 1 and 2, the clamping unit 1 shown in FIG. 3 does not have a separate locking device 8, but the pistons of the pressure pads 7 can be moved continuously in the cylinders. Here, the maximum dimensioning of the melded part is limited by the maximum stroke of the pressure pads 7. The pressure pads 7 can be used here, both, for the rapid stroke and for the application of the holding force.

In the clamping unit 1 shown in FIG. 4 a central piston-cylinder unit 14 is provided for moving the second meld clamping plate 4, and for applying the holding force. Here, the maximum dimensioning of the molded part is limited by the maximum stroke of the piston-cylinder unit 14.

The embodiment shown in FIG. 8 allows the production of endless molded parts. For this purpose, a holding device 15 is provided, which holds the injection melded pad 10. In this embodiment, the holding device 15 is designed as a mandrel. The holding device to is attached to the first mold clamping plate 3 via the first tool part 8 and/or the melt distributor 18.

The tool shown with a first fool part 8 and a second tool part 9 is used as an example for producing formed tubes with straps, beads, ribs or elements that generally deviate from the contour.

A melt distributor 16 is arranged on the first mold clamping plate 3, which distributes melt provided by an injection unit 13 not shown around the entire circumference of that part of the cavity, which is formed in the first tool pad 8. In this embodiment, the second tool part 9 has a horizontal parting plane, relative to which the second tool part 9 formed here in the form of two jaws can be opened (in general, the second tool part 9, for example, consists of at least two parts that can be moved away from each other).

The first and second tool parts 8, 9 are completely filled with melt in the position of the second mold clamping plate 4 shown in FIG. 5 a, relative to the first mold clamping plate 3. Injection continues while the second mold clamping plate 4 is moved away from the first mold clamping plate 8 at a speed, which is open loop-controlled or closed loop-controlled, resulting in an increasing gap 12 between the first fool part 8 and the second tool part 9. The speed at which the second mold clamping plate 4 is moved away from the first mold clamping plate 3 is preferably open loop-controlled or closed loop-controlled in such a way that the filling of the cavity is guaranteed. The closed loop-control is preferably force-controlled.

Optional temperature control of tool parts 8, 9 ensures that the melt is sufficiently solidified before it leaves the cavity.

After reaching the end position of the second mold clamping plate 4 relative to the first mold clamping plate 3 as shown in FIG. 5 b, the injection process is interrupted. The second tool part 9 is opened, and the second mold clamping plate 4 is moved hack to the position shown in FIG. 8 a. The already solidified section of melt passes through a passage opening 17 arranged in the second mold clamping plate 4. The injection process is continued until either the molded part with the desired length is produced, or the second mold clamping plate 4 returns to the position shown in FIG. 5 b. If the desired length of the molded pad is still not reached, the process is repeated until the desired length of the molded part is reached.

The parts of the second tool pad 9 can be designed in such a way that they prevent the injection-molded part from advancing by frictional connection, so that the latter can be determined purely by the movement of the second mold clamping plate 4.

The parts of the second toot part 9 can he provided with additional cast-on elements for producing a form-fit with the solidified section of the melt (see FIG. 5b ).

In FIG. 5b if can he seen that the upper part of this Fig. is provided with a runner, and—if this is desired—can be supplied with melt via its own injection unit 13. This additional cavity can be used, for example, to injection-farm surface structures, such as ribs, onto the part.

The parts of the second tool part 9 can he provided with sliders 18, which can press into the melt in order to achieve a form-fit with it.

The sprues of the molded part can be injected by a separate injection point or by a valve.

A trimming device (e.g. cutting device) can be provided for trimming the molded part, wherein the trimming can take place e.g. at regular time intervals. The trimming device can be arranged, for example, between tool parts 8, 9.

LIST OF REFERENCE SIGNS

1 clamping unit of a molding machine

2 machine bed

3 first mold clamping plate

4 second mold clamping plate

5 tie bar

6 locking device

7 pressure pad

8 first tool part

9 second tool part

10 injection-molded part

11 sprue

12 gap

13 injection unit

14 piston-cylinder unit

15 holding device

16 melt distributor

17 passage opening in the second mold clamping plate

18 slider 

1. A method for producing a molded part, in which melt is inserted into a cavity of an openable molding tool, wherein the molding tool comprises a first tool part and a second tool part of which the first tool part is mounted to a first mold clamping plate, and the second tool part is mounted to a second mold clamping plate, which is arranged movably relative to the first mold clamping plate, and wherein the cavity has a zone arranged in the first tool part and a zone arranged in the second tool part, and is closable and openable by moving the second mold clamping plate relative to the first mold clamping plate wherein melt is inserted into the cavity, and the first tool part and the second tool part are moved away from each other during the insertion or after the insertion of the melt by moving the second mold clamping plate relative to the first mold clamping plate so far that in the first tool part or in the second tool part, an at least partial clearance of the first or second zone of the cavity takes place, and a gap is formed between the first tool part and the second tool part wherein further melt is inserted into the cleared zone of the cavity wherein the gap is bridged by an at least already partially solidified section of the melt and a holding force is transmitted from the second tool part through the at least already partially solidified section of the melt bridging the gap to the first tool part.
 2. The method according to claim 1, wherein the second mold clamping plate by means of tie bars, the pressure pads which exert a pressure on the tie bars, can be acted upon with a holding force, relative to the first mold clamping plate, wherein the pressure pads have a stroke, and the gap is formed by a stroke movement of the pressure pads or by a rapid-stroke mechanism.
 3. The method according to claim 2, wherein after the insertion of a first amount of melt the tie bars are locked by a locking device, relative to the second mold clamping plate, and the locking device is opened after the stroke of the pressure pads has been exhausted and the tie bars are moved so far by the pressure pads that the stroke of the pressure pads is available again and the locking device is closed and a second amount of melt is inserted into the enlarged zone of the cavity
 4. The method according to claim 1, wherein the injection-molded part is held by a holding device, and the already solidified section of the melt passes through a passage opening arranged on the second mold clamping plate.
 5. The method according to claim 1, wherein the moving away of the first tool part and the second tool part from one another is carried out in a parallelism-controlled manner.
 6. The method according to claim 1, wherein the second mold clamping plate is moved relative to the first mold clamping plate by means of a piston-cylinder unit, and the gap is formed by a stroke movement of the piston-cylinder unit.
 7. The method according to claim 1, wherein the melt required for the manufacturing of the molded part is provided by the same injection unit, and inserted into the cavity.
 8. The method according to claim 7, wherein the injection unit operates discontinuously.
 9. The method according to claim 1, wherein the melt required for the production of the molded part is provided by several injection units, and inserted into the cavity.
 10. The method according to claim 1, wherein additional power transmission elements are used for partial transmission of the holding force. 